Presently, when air bag covers are provided in automobiles on the driver side of the vehicle, the air bag is stored in the steering column behind an air bag cover. During automatic inflation of the air bag, the air bag cover moves away from the steering column to permit its safety function between the steering column and the operator of the vehicle.
Recent practice in the automotive industry is utilization of all plastic fabricated air bag covers. Conventional air bag covers used in conjunction with occupant restraint systems often include noticeable or visually perceptible break seams or scores disposed on the exterior surface of the air bag cover. The break seams or scores represent selected weakened surfaces where the inflating air bag initially separates or breaks through the air bag cover and moves away from the steering wheel to perform its safety feature.
U.S. Pat. No. 4,325,568 issued to Clark et al. discloses a modular occupant restraint system including an inflator, a cushion, a container for the cushion and an air bag cover for the container assembled as a module. Clark et al. further discloses use of score lines that are visually perceptible from a front view of the air bag cover as it is operably mounted on the steering wheel of the automobile.
U.S. Pat. No. 5,085,462 issued to Gaultier discloses an air bag and vehicle horn switch assembly. The assembly of Gaultier also discloses use of an air bag cover including visually perceptible exterior break seams or score lines in the operable mounted position within the vehicle.
U.S. Pat. No. 5,186,490 issued to Adams et al. discloses a cover for an inflatable restraint system for a motor vehicle which contains a slot in the upper wall thereof into which a thin or membrane type switch assembly is inserted. Adams et al. further discloses an air bag cover having an injection molded thermoplastic upper wall and a soft outer cover exposed to the interior of the vehicle manufactured from urethane, vinyl or polyester. The outer cover completely encompasses and overlaps the upper wall structure and uninflated air bag forming two structures the air bag must exit to carry out its function.
Current trends in the automotive manufacturing industry are oriented towards providing, clean aesthetically pleasing outer surfaces within the interior of the automobile. Inclusion of extraneous exterior break seams or score lines that are perceptible from an occupant's viewpoint in front of the steering wheel detracts from the overall appearance of the interior of the automobile.
It is also known that the provision of noticeable exterior break seams or score lines that are designed for aesthetic purposes is very difficult to achieve as the final design obtained must satisfy engineering requirements related to inflation and exit of the air bag. Thus, use of visually noticeable exterior outer score lines is limited to known score line designs such as the "H" shaped score lines disclosed in U.S. Pat. No. 5,085,462 to Gualtier.